High efficiency retroreflecting polarizer

Abstract

A retroreflecting polarizer comprises a pair of first and second substrates, each essentially like the other, each having a planar first surface and a structured second surface, whereby the structured second surface comprises a linear array of isosceles prisms with faces formed at an angle of approximately tan -1 (1/n) with respect to the planar first surface. The respective structured second surfaces of the first and second substrates are mated with one another through one or more of substantially uniformly thick layers, all of the same optical material, that are parallel to the structured surfaces. The structured surfaces and layers are separated from one another by associated air gaps. The interfaces formed within the retroreflecting polarizer satisfy Brewster's condition for a light beam normally incident upon the retroreflecting polarizer which is split into a σ-polarized retroreflected light beam and a substantially π-polarized transmitted light beam.

I claim: 
     
       1. A retroreflective polarizer, comprising: a. a first substrate of optical material having a planar first surface and a structured second surface, whereby said structured second surface comprises a linear array of isosceles prisms arranged side by side and having faces formed at an angle of approximately tan -1  (1/n) with respect to said planar first surface, where n is the index of refraction of said optical material;   b. a second substrate essentially like said first substrate; and   c. one or more layers of said optical material disposed between said structured second surfaces of said first and second substrates, wherein the surfaces of said layers are essentially parallel both to one another and to said structured second surfaces of said first and second substrates.   
     
     
       2. A retroreflective polarizer as recited in claim 1, wherein said layers are adjacent one another and said structured second surfaces of said first and second substrates are each adjacent one of said layers. 
     
     
       3. A retroreflective polarizer as recited in claim 1, further comprising associated air gap proximate to one or more of the surfaces of said layers. 
     
     
       4. A retroreflective polarizer as recited in claim 1, wherein the substrates are sealably connected to one another at the periphery of said substrates. 
     
     
       5. A retroreflective polarizer as recited in claim 1, wherein the said optical material is flexible. 
     
     
       6. A retroreflective polarizer as recited in claim 1, wherein said layers are secured to one another and to said first and second substrates with an optical adhesive at a plurality of locations. 
     
     
       7. A method of polarizing light, comprising a. directing a beam of light in a plane of incidence onto a planar first surface of a first substrate of optical material;   b. transmitting said beam of light through said first substrate;   c. reflecting a portion of said beam of light from a second surface of said first substrate such that the reflected beam is substantially polarized normal to said plane of incidence;   d. refracting the substantially remaining portion of said beam of light by a medium having an index of refraction of essentially one;   e. performing the following two operations one or more times;   f. reflecting a portion of said substantially remaining portion of said beam of light from the first surface of a layer of said optical material such that the reflected beam is substantially polarized normal to said plane of incidence;   g. refracting the substantially remaining portion of said beam of light by a medium having an index of refraction of essentially one;   h. reflecting a portion of said substantially remaining portion of said beam of light from the second surface of a second substrate of said optical material such that the reflected beam is substantially polarized normal to said plane of incidence;   i. refracting the substantially remaining portion of said beam of light through said second substrate.   
     
     
       8. A method of manufacturing a retroreflecting polarizer, comprising: a. constructing a first substrates from an optical material having a planar first surface and a structured second surface, wherein the structured second surface comprises a linear array of isosceles triangles arranged side by side and having faces formed at an angle of approximately tan -1  (1/n) with respect to said planar first surface, where n is the index of refraction of said optical material;   b. constructing a second substrate essentially like said first substrate;   c. constructing one or more layers from said optical material, each said layer having essentially uniform thickness and structured so as to mate between said structured second surfaces of said first and second substrates; and   d. forming an assembly by assembling said one or more layers between said structured second surfaces of said first and second substrates.   
     
     
       9. A method of manufacturing a retroreflecting polarizer as recited in claim 8, further comprising the step of sealing the periphery of said assembly.